This invention relates to a mobile paper shredding system. More particularly, this invention relates to methods and apparatus used in shredding large volumes of paper generated either by large businesses or multiple businesses located close together. It is primarily adapted for use in urban and suburban areas, although benefits of the system can be utilized at any location where there is a need for mobile paper shredding services.
Truck-mounted paper shredding equipment is in common use today, primarily in urban environments. Typically, the shredding equipment is mounted on the bed of a truck which moves among office buildings to collect discarded office paper. This waste paper is fed into an opening or hopper of the shredding system, where it passes through a shredding apparatus, such as a hammer mill. Paper shredded by the hammer mill is then fed into a container typically located at the rear of the truck where it is stored until the container may be emptied. In this manner, discarded paper can be effectively compressed into a smaller volume of space for more efficient transportation to a municipal landfill or recycling center.
Problematic in the design of mobile paper shredders for use in an urban or suburban environment is the size and configuration of the equipment. Obviously, it is desirable for a shredding system to have a large storage capacity to reduce trips to the landfill or recycling center. It is also desirable to have a powerful shredding system to process waste paper as quickly as possible. However, these needs are often in conflict. With mobile shredding systems, large storage capacity reduces the space available for powerful shredding equipment and powerful shredding equipment typically reduces the available storage space for shredded paper. For example, in known mobile shredding systems, the paper feed and shredding equipment is mounted along the longitudinal axis of the truck bed, typically to allow for simple and direct power transfer from the drive train of the truck. Unfortunately, for a given size truck bed, the length of the shredding equipment directly affects the amount of available storage capacity for shredded paper. Increasing the length of the shredding equipment, to increase throughput of paper, directly decreases the amount of available storage.
Yet another problem with known mobile paper shredders is a lack of mobility in confined spaces. Indeed, in many large cities, buildings are separated by narrow alleys and loading docks, or other commercial receiving areas are located either in these alleys or, perhaps, underground garages. In either case, large trucks cannot easily maneuver into these confined spaces. As a result, the demand is great for smaller, more efficient configurations without sacrificing storage capacity. Besides the configuration and layout of the equipment, a further limiting factor on the ability of a mobile shredding system to operate in confined spaces is the lift system. In some known mobile shredding systems, the lift systems move waste paper containers through a fixed radius path away from the body of the truck until the waste paper container is positioned over an opening or hopper for the shredding system. Such lift systems require substantial lateral space around the perimeter of the truck body to allow the lift system to operate. A further problem is created when a loading dock is used. In such a case, the truck must be parked a precise distance from the loading dock in order for the lift system, in mid-stroke, to pick up a waste paper container from the loading dock.
Yet a further problem of paper shredding systems is generation of unwanted dust. While creating dust during paper shredding is inevitable, the creation of dust can be controlled. In known systems, dust is created due to shredder blades beating on paper, or paper beating on paper, rather than blades shredding paper. In such circumstances, paper fibers are exposed and excessive dust is created. These problems result from, among other things, an extended paper path between the infeed of paper and the shredding apparatus, overfeed of paper into the shredding apparatus, a poorly designed shredder or, perhaps, a combination of these factors.
Overfeed and jamming of shredding apparatus can be another major problem. This can cause significant delays and, in a worst case, can cause motor burn out, which can result in still further delays, substantial costs associated with replacement equipment, and even lost business and associated lost revenues.
The present invention relates to a mobile paper shredding system transversely mounted on a truck bed. Generally, the shredding system is designed and configured to be compact and lightweight such that a smaller truck may transport and operate the system. The system enclosure is aluminum reinforced plastic and all parts are steel or aluminum except for the shafts and components of the mill and augers and associated bearings and support structure.
The mobile paper shredding system comprises a lift system, a first feed system, a shredder, a second feed system, and a storage container with a sliding wall to remove shredded paper, all of which are installed within a truck bed-mounted enclosure. The lift system is used to elevate and dump the contents of a waste paper container into an opening in the top of the enclosure above the first feed system. The first feed system delivers the waste paper to the shredding equipment, a hammer mill. The hammer mill shreds the waste paper when the paper is struck by rotating blades on the hammer mill shaft against a separator plate. The shredded paper, when properly reduced in size, passes through a screen comprising multiple two-inch diameter openings. The second feed system or packer then packs the shredded paper passing through the screen into a waste container at the rear of the enclosure through an access door. Once the rearward portion of the enclosure is filled to capacity, the load is transported to place for disposal, typically a recycling center. The shredded paper is removed from the enclosure by advancing a rolling wall towards the rear of the enclosure which forces the packed, shredded paper from the enclosure.
The lift system of the preferred embodiment is constructed from aluminum to decrease the weight of the unit. It is designed with a limited profile, fitting within a small space of the overall enclosure to further enhance the paper shredder system""s adaptability to be used in confined areas. The lift system is designed to operate in three stages: lowering to street level; elevation of the paper container substantially vertically along the side of the truck, rather than in a fixed radius path; and dumping of the container into the infeed opening of the shredding system. This further enhances use in confined areas. In addition, the configuration of the lift arms allows any of the three stages to be operated independently. In this way, a paper container may be engaged directly off an elevated loading dock, rather than from street level, by implementing only the second and third stages of the lift system. The result is a more efficient and compact lift system.
A feed control system is designed to prevent overloading the hammer mill. A key parameter is ensuring that the output of the hammer mill is greater than the input of the first feed system. Maintaining this relationship increases the capacity of the system by guaranteeing efficient operation of the hammer mill. In this regard, the feed control system employs a monitoring and feedback system to prevent overloading the hammer mill. More specifically, the rotational speed of the hammer mill is directly monitored. If the revolutions per minute of the hammer mill fall below a threshold amount, for example, 1800 rpms, a switch is triggered which stops the paper infeedxe2x80x94the first feed system. Stopping the first feed system allows the hammer mill to shred a sufficient amount of paper to decrease strain on the motor. Once the overfeed is eliminated and the rotational speed of the hammer mill surpasses the threshold, the monitoring system restarts the first feed system and paper processing continues uninterrupted.
The hammer mill is mounted transverse to the truck bed. In the preferred embodiment, the working length of the hammer mill is approximately 46 inches, significantly longer than the known art. It includes 15 discs spaced equally along the length of the mill shaft. Each disc has four blades spaced equally around the circumference of the disc on alternating sides of the disc. The longer mill length increases the volume of paper that can be processed without sacrificing storage capacity. The longer length also helps reduce dust produced during operation because lower feed speeds can be maintained while processing an equivalent amount of paper. The blade width dimension (xc2xc inches) is reduced from prior mill systems known to the inventor. This narrow profile results in improved shredding and less beating of the paper by the blades, and hence, less dust production.
The orientation of the first feed system to the hammer mill also improves performance. As configured, the first feed system delivers paper directly to the hammer mill, without an extended paper path. The paper exits the first feed system directly into the contact region between the mill blades and the separator fingers. The paper is promptly shredded when forced between the mill blades and the separator fingers. The close spatial relationship between the first feed system and the hammer mill ensures the paper is shredded only by metal to paper contact. In the prior art known to the inventor, where the feed mechanism is separated from the hammer mill by an extended distance, the volume of waste paper can increase, causing more paper on paper contact. This can cause much of the paper""s fiber to be broken down and create significant dust. Excessive dust is undesirable since many recyclers will reject dusty loads due to health hazards of paper dust inhalation. Excessive dust also can foul mechanical systems and requires constant cleaning to maintain the systems in proper operating conditions.
The second feed system or packer is a modified version of a silage (bag) packer. The packer component has been adapted from the silage packer to include a comb with wedges. The packer is also mounted transverse to the truck bed and, in the preferred embodiment, its length matches the length of the hammer mill. The blades of the packer are staggered through a 360 degree configuration around the packer to enhance processing of shredded paper without jamming. The staggered blades rotate through the gaps between fingers of a comb member. Wedges assist in stripping paper away to prevent jamming of the blades in the comb fingers. Both the blade and wedges may include serrations on the paper contact surface to improve paper handling, including packing the shredded paper more densely.
A wetting system may also be included as part of the packer to increase density of packed paper and to reduce dust. In this regard, water is added to the trough formed at the bottom of the packer. As the blades of the packer rotate and move shredded paper through the water, the paper absorbs the water, allowing it to be packed more densely and causing dust to adhere to the shredded paper. As an additional benefit, the water reservoir used to supply water to the trough is also available to supply water to a sprinkler system in the unlikely event a fire is started somewhere within the housing.
A moving wall (or unloading wall) is constructed of aluminum with an access door adjacent to the packer. The storage area of the enclosure is unloaded by advancing the moving wall towards the rear of the truck thereby forcing the packed, shredded paper from the enclosure. The moving wall is provided with wheel-like rollers which ride along rails mounted on the truck bed. The moving wall may be guided by bearings which travel within grooves mounted in the compartment walls. The moving wall is advanced by an electric motor powered shaft and gear which is connected to the moving wall.
The design of the mobile paper shredding system, as described above, may be mounted on the bed of a 26,000 pound truck with a bed length of 20 feet. The size of the truck, again, lends itself to better maneuverability within constrictive areas, such as urban alleys and loading docks. Additionally, the smaller truck size permits operation of the truck and system without a Commercial Drivers License. The above system is capable of shredding up to 8,000 pounds per hour of paper.
The shredder system is housed within approximately the front five feet of the enclosure, leaving approximately fifteen feet of the enclosure for containing the shredded paper. Access doors are provided at various locations on the enclosure. One is located adjacent to the shredding system and power train for the shredding system on the driver""s side of the enclosure. Another is located rearward of the moving wall when the moving wall is in its forward most position, also on the drivers side of the enclosure. These enclosures allow the operator or other maintenance personnel access to essentially all areas of the system to perform any necessary work. The rear of the enclosure comprises double doors that allow the shredded paper to be removed.